Progressive lenses, also known as PAL (progressive addition lens), are widely used, especially by patients with weak eyesight in both reading and distance visions, like many presbyopes. There are different designs of progressive lenses produced by various manufacturers. As is known in the art, the two main features characterizing all designs of the progressive lens are optical power distribution and distortion distribution within the lens. FIGS. 1A and 1B illustrate two different examples, respectively, of these features for the same lens. There is practically no way of eliminating all the distortions.
The example of FIG. 1B presents a typical distortion map of a standard progressive lens. The lens has prescribed parameters of optical powers required for a patient's distance and reading visions and also cylinder parameters when necessary. The lens is formed with four main zones, wherein zone 2 is a far vision zone corresponding to the patient's distance vision, zone 3 is a near vision zone corresponding to the patient's reading vision, zones 5 are peripheral zones of concentrated optical distortion, defining a fourth zone 4 therebetween which is stretched between zones 2 and 3. This fourth zone 4 is a narrow passage, called "corridor", which is free of distortions and in which power varies continuously. All these features of the progressive lens are well known per se, and, therefore do not need to be described in detail, except to note that each standard semi finished PAL is characterized by its "addition" value (ADD), defined as the difference between the far and near vision powers.
The entire process conventionally carried out for providing a patient with
spectacles includes the following stages:
(1) determining for each eye values of the optical power required for the patient's reading and distance visions; PA1 (2) selecting for each eye a semi finished lens of a suitable standard kind according to its "addition" value, and processing the inner side of the semi finished lens according to the prescribed values of the optical power and cylinder when necessary; and PA1 (3) cutting the lens, and mounting it in the frame of the spectacles (previously chosen by the patient) in such a position that the pupil location of the patient for far vision matches a Fitting Cross marking on the lens. PA1 the Fitting Cross 6A which is the recommended position to mount the lens relative to the patient's pupil in distant vision; PA1 a horseshoe marking 6B, which is the location recommended by the manufacturer for measuring the far vision power of the lens; PA1 a Horizontal Fitting Line 7, which is the reference orientation line that should be horizontal when the lens is mounted in the frame; and PA1 a circle 8 is the center of the near vision zone, namely the location where the patient's line of sight is expected to pass when the patient reads. PA1 (a) a target member with reading material on its outer surface, wherein said target member is orientable by the patient in a manner corresponding to his natural reading position; and PA1 (b) a video camera mounted within said target member and disposed such that the patient's eyes are located within the depth of field of the camera, while said reading material is located out of the camera's depth of field, the camera thereby acquiring an image of the patients' eyes in a frame of his spectacles, whilst the patient reads said reading material in his natural reading position, enabling to determine an intersection of a line of sight of each patient's eye with a plane defined by the frame relative to the frame. PA1 (i) determining a location of intersection of a line of sight of the patient's eye at natural reading mode with a plane defined by the frame of the spectacles relative to said frame, wherein said determining is performed at the patient's habitual reading position by using a device comprising: PA1 (ii) determining the distributions of said optical power and optical distortions of the progressive lens; PA1 (iii) analyzing data indicative of the determined location of intersection of the line of sight of the patient's eye at said reading mode with the plane defined by the frame of the spectacles relative to said frame, and data indicative of the determined distributions of said optical power and optical distortions of the progressive lens, for determining whether an optimal positioning of the lens via at least one of a horizontal translation, a vertical translation, and a rotation of the lens relative to said frame can be achieved; PA1 (iv) if said optimal positioning of the lens cannot be achieved, replacing the prescribed lens by another lens having at least one different parameter as compared to that of said prescribed lens; and PA1 (v) if said optimal positioning of the prescribed lens can be achieved, generating data representative thereof and using said generated data for mounting the lens into the frame PA1 a device for determining a location of intersection of a line of sight of the patient's eye for the natural reading mode with a plane defined by the frame of the spectacles relative to said frame, wherein said device comprises: PA1 a device for determining the distributions of said optical power and said optical distortions of said progressive lens; PA1 a processor capable of analyzing data indicative of the determined location of the intersection of the line of sight of the patient's eye at said natural reading mode with the plane defined by the frame of the spectacles relative to said frame, and data indicative of the determined distributions of said optical power and optical distortions of the progressive lens, and generating data indicative of an optimal positioning of the lens relative to said frame; and PA1 a device for positioning said progressive lens via at least one of a horizontal translation, a vertical translation, and a rotation relative to said frame for mounting the lens into the frame at said optimal position of the lens.
As illustrated in FIG. 2, the Fitting Cross 6A is a marking on the lens provided by the lens manufacture, and indicates the position of the far vision point that should be located in front of the patient's pupil center when looking at a far object. Generally, the only apparent relevant information about the lens supplied by the manufacturer to the optician is in the form of the following four standard stamped markings on the surface of the lens:
In FIG. 2, numbers 9A and 9B designate "real" pupil locations (unmatched) for distance and reading vision, respectively, as found for a specific individual. The borders of the distortion zones 5 shown in dashed lines are typically unknown to the optician (concealed from view), and can only be detected by special instruments, mostly available to manufacturers, but still not to opticians. The location of the distortion zones 5 cannot practically be determined by the conventional equipment the optician has at his disposal.
Thus, by using the conventional techniques for adjusting lenses while mounting them into the spectacles' frame, the borders of the distortion zones 5 are not taken into consideration. Obviously, if while reading, the patient, for any reason, even slightly misses the recommended reading zone 8, his line of sight might pass through the highly distorted zone 5 and/or not at the appropriate power. This may result in blurred vision, eyestrains, focusing difficulty and itchy eyes. Reasons for missing the reading zone may be, for example, the result of erroneous fitting of the lens into the frame or, in other cases, when the patient holds the reading object (e.g., his book) too high or too low, or too far or too close from the position where the lens designer assumed it to be.
Although the rate of success in fitting progressives was appreciated to be relatively high according to past surveys, newly released independent surveys disclose that one out of three presbyopes is not satisfied with his PAL glasses. These unsatisfied patients use their progressive spectacles mainly for far sight and occasionally for near vision, but not for actual reading. For reading, they constantly turn to their usual reading glasses. The discrepancy between past and recent surveys is probably due to the fact that past surveys relied on the rate of progressives returned to the practitioners as a sole indicator. As it turned out, many unsatisfied customers for various reasons failed to return their unsuccessful progressives to their dispensers.
Apparently, one of the most significant rationale for the unsuccessful adaptation of a patient to his PAL glasses, is that the design of the PAL is performed according to statistical data. For example, it is well known that for most people, reading distance is about 35 cm, and, accordingly, the design of most progressives relies on this presumption. However, older individuals may, over time, develop different reading habits by positioning the reading material in various distances and angles relative to the body. This may have a devastating effect on the functioning of the progressive lens. The problem becomes even more complex, because for this age group, it is difficult, often painful, and sometimes even impossible, to change their reading habits.
Evidently, it is impractical to custom design a lens for every patient. On the other hand, very little can be done by the optician during the lens' mounting process, if he does not receive full and accurate information about the lens, as well as about his patient's habits. Moreover, even with enough information about the lens, the optician should be provided with means to apply a set of considerations and reasoning as to how many distortions and power errors should be allowed in order to ensure optimal fitting.
The typical procedure performed by the optician is illustrated in FIG. 3. The optician measures the far vision pupil's location relative to the selected frame independently for each lens, or alternatively derives this information from the measured inter pupillary distance. The respective data, as well as the spectacles' frame itself is input into a so-called "edger" device. The construction and operation of the edger are known per se, and therefore need not be specifically described, except to note that the edger is typically used for the circumferential cutting of a lens to fit the frame. Upon detecting that the pupil location for the distance vision overlaps the Fitting Cross 6A marked on the lens, the optician operates the edger for cutting the lens.
It is often the case that such a process of adjusting progressive lenses for a patient's spectacles renders unsatisfactory results, and many patients feel uncomfortable with their new spectacles for a long time. One of the reasons for this is that the adjustment is actually solely based on the distance vision parameters, while those of reading vision are completely ignored. This follows from the basic presumption that the patient, in the end, will adapt his reading habits to his lenses. Unfortunately, it seems that for a considerable number of patients, this never happens.
This limited success of PAL fitting was not unknown to those skilled in the art, and for many years efforts have been made to encourage "individual fitting", i.e., adapting the lens to the individual's parameters. Devices have been developed to provide the optician with more information concerning his patient and specifically, his pupils locations for near objects. Although various different approaches were utilized in developing these devices, yet they can generally be divided into three main groups.
Devices of the first and most popular group are known as "pupilmeters". These instruments deal exclusively with horizontal pupils decentration for near objects, and specifically for objects that are at a preset distance (usually 40 cm) from the patient's eyes. The object employed is a point light source that is translated, optically or physically, to this preset distance. The pupils' locations are measured mostly with good accuracy. However, these instruments cannot perform the measurement of an eye's drop. One of the latest models of this group, which is considered as the most advanced, is disclosed in U.S. Pat. No. 5,691,799. In distinction to other pupilmeters, this device is capable of measuring the pupils' horizontal decentration, while the patient wears his glasses. In other words, pupils locations are measured relative to the spectacles frame. However, the eyes' drops are still not measured. Since this device is stationary, rigidly mounted on a table with a patient's chin rest and head support, no reading can actually take place during measurement, and obviously not natural reading (i.e., in the natural reading position of the patient). Thus, although devices of the first group yield very accurate horizontal decentration results, the rate of success in fitting has not been meaningfully changed.
Devices of the second group do evaluate the eyes' drop. To this end, these devices utilize a point light source that is mounted somewhat lower than eye level. One of the devices of this kind is disclosed in U.S. Pat. No. 3,454,331. This device is positioned on a table (a "desktop model"), whereby the patient and optician sit at opposite sides of the table. The optician has an active role in operating the device by aligning it through a viewfinder (optical sight). The near object target is a point light source located a little higher than the table level, and the patient is asked to focus his eyes on the light source. During this procedure, the optician, through the viewfinder, aligns the device to capture the eyes' image with a conventional camera. This device advantageously measures a certain eye's drop. However, this measured eye's drop is a dictated one, and not necessarily the habitual reading eye's drop, because of its dependence on the table's height, the chair height and the patient's height. It works under the presumption that the patient will hold his book (or other reading material) on the table at a preset distance and angle. Additionally, the light source does not simulate a reading target, and the device cannot in any way be transformed to simulate natural reading, for example, by letting the patient hold the device in the most comfortable position and replacing the light source target by a reading target. Because of the optician's active role during measurement, it is impossible for the optician to stick his eye to the viewfinder while the device is held unsteadily by the patient.
The basic presumption of the above approach, which was also used in similar devices developed later, is that the patient's eyes' drop is not a personal parameter that should be learned and measured, but rather a controllable property. In other words, the patient is expected to adapt his eyes' drop to the given target, or at least be educated to do so whilst wearing his PALs. In view of the latest surveys, it seems that this approach is apparently inaccurate for a considerable number of presbyopes.
FR 2384232 discloses a simpler and improved version of the above device. This improved device is lightweight and has more convenient optical sight. However, it is still designed like a desktop-device, and cannot be transformed to a "handy" or "moveable" device, since it requires continuous alignment by the optician. FR 2672792 discloses an even more improved device, where optical sight is replaced with a camera. Similarly, it is designed like a desktop system with a light source target and a dictated reading angle. Deviation from this angle moves the patient's image out from the camera's field of view.
A different approach is utilized in systems of the third group. Such systems are disclosed, for example, in U.S. Pat. Nos. 4,368,958 and 5,640,775. Here, a device is mounted on the spectacle's frame, and the pupil's positions relative to the frame are measured. According to the technique of U.S. Pat. No. '958, the patient is asked to slide small opaque targets in front of his eyes until his viewing object, far or close, is obscured from view. The targets' positions, which represent his pupils' locations, are then measured. U.S. Pat. No. '775 discloses a similar approach, but here, the targets comprise small illuminated fiber optics. The targets appear as bright light spots in front of the patient's eyes. In distinction to U.S. Pat. No. '958, this device might utilize reading material. However, this device is unable to fulfill the basic conditions necessary to create a natural reading environment. Certainly, for many patients, it might be almost impossible to simulate their habitual reading while bright lights shine in front of their eyes.